1. Field of the Invention
The present invention generally relates to an accessory adapted to be mounted upon or attached to a folding ruler, and more particularly to an accessory adapted to be mounted on a folding ruler having a plurality of rigid sections with graduations marked thereon. The ruler includes outer sections and intermediate sections hinged to one another adjacent their ends, and the accessory is adapted to be attached to one of the end sections, rather than one of the intermediate sections. The accessory generally comprises a bar and a sheath adapted to hold the bar and retain the end section of the folding ruler to which the accessory is attached.
2. Description of Prior Art
Folding rulers are well known and conventional and generally comprise two end or outer sections and one or more intermediate sections positioned between the outer sections. In one preferred embodiment, the outer sections have lengths of approximately 22 cm., while the intermediate sections have lengths of approximately 24 cm. In practice, the end sections have usable lengths of 22 cm., while the usable portions of the intermediate sections are also 22 cm.; the difference between the usable portion of the intermediate sections and their length is 2 cm., which distance enables hinge pins to be received for hinging adjacent sections to one another. In other words, this is a portion of each section which cannot be used in measuring a distance.
Such rulers make it easy to measure exterior lengths, because when they are unfolded, they are relatively rigid. On the other hand, these rulers are not practical for measuring interior distances and lengths, and are particularly unsuitable for measuring the length of a space located between opposed parts or surfaces, because in most cases such a space does not correspond to a multiple of the length of the sections. In other words, it is difficult to precisely measure an interior distance between two surfaces because the sections come in multiples of a distance, i.e., in the above preferred embodiment, 22 cm., and it is unlikely that a distance being measured could be a precise multiple of 22 cm. Accordingly, it will be necessary to use only a portion of one of the ruler sections and to therefore judge or estimate the precise distance.
One ruler has been proposed to solve this problem, and includes one ruler end section which comprises a longitudinal central groove having a dove-tail cross-section and a graduated, smaller ruler of a corresponding cross-section adapted to slide therein. By this arrangement, spaces can be measured by sliding the small ruler until it butts against one of the portions or surfaces bounding the distance being measured, while the end of the main ruler butts against the other portion or surface.
Such an arrangement, however, is disadvantageous for a number of reasons. The sections must necessarily be formed relatively thick in order to permit the formation of a groove and the insertion of the sliding member into the groove. The smaller ruler must be as thin as possible, while also being sufficiently strong so as to resist twisting and breakage; accordingly, this ruler can only be formed from metal. The use of a small metallic ruler, however, is not advisable in measuring distances in electrical applications. Such a ruler is expensive to manufacture, and not practical in usage. Further, any measurement read from the small ruler must be added to the measurement made from the main ruler, which introduces an additional source of error into any measurement or computation.